Food Allergy and Intolerance

food allergy

An allergy is a response by the body's immune system to something (called an allergen) that is not necessarily harmful in itself. Certain people are sensitive to this allergen and have a reaction when exposed to it.

What is a food allergy?

A food allergy is an abnormal reaction of the body's immune system to a particular food. This tends to cause unpleasant and unwanted effects (symptoms).

What is food intolerance?

Food intolerance is NOT the same as food allergy. Many people incorrectly use the words interchangeably. A food allergy is when the body's immune system reacts abnormally to specific foods. No allergic reaction takes place with a food intolerance. People with food intolerance may get digestive symptoms such as diarrhoea, bloating and stomach cramps. In food intolerance, the symptoms can be caused by various problems. Some examples are:

Lactose intolerance causes diarrhoea and abdominal symptoms (bloating and pain) after milk is drunk or dairy products are eaten. It happens because of a deficiency of lactase, an enzyme in the body that digests lactose (the sugar) in milk.

Direct effects of foods and additives may directly affect the body and cause symptoms. For example, some people find that the food additive monosodium glutamate (MSG) causes flushing, headache, abdominal pains and bloating.

Differences between food allergies and food intolerance

The symptoms of food intolerance occur usually a few hours after eating the food. Allergic reactions happen much more quickly. With an allergy, even a tiny amount of the food can cause an allergic reaction to take place. Food intolerances are never life-threatening. Some allergies are as they can cause anaphylaxis and are thus life threatening.


Food allergy

  • Atopic eczema (classical eczema) that is seen in allergy-prone (atopic) families - often those with hay fever and asthma too.
  • Gastro-oesophageal reflux which is vomiting that is generally effortless.
  • Loose and/or frequent stools (poo).
  • Constipation.
  • Blood or mucus in the stools.
  • Redness around the anus.
  • Tiredness.
  • Pallor.
  • Poor growth.

Food intolerance

  • Bloating and abdominal pain.
  • Diarrhoea or loose stools.
  • Skin rashes and itching.


Specific tests

If it is thought that you have an IgE-mediated allergy, there are two main types of test that can be done:

  • Skin prick test. This is usually done in a specialist hospital allergy clinic. A small drop of liquid containing the food substance is placed on the skin of the forearm and a needle is used to prick the skin, through the droplet. This allows the food to enter the skin. After a period of time, the droplet is wiped off and the skin is read.
  • Blood tests. Blood tests can detect if your blood contains specific IgE antibodies. So, if you had allergic reactions to peanuts, your blood might contain antibodies to peanuts. This test is called RAST, which stands for radioallergosorbent test.

Elimination and challenge

If a non-IgE food allergy is suspected, elimination and challenge can be used to try to confirm the diagnosis of allergy. This is only really appropriate when it seems clear which foodstuff is causing the problem. The food should be excluded from the diet completely for 2-6 weeks, to see if symptoms improve. After this time, the food should be reintroduced, to see if symptoms return.

Management of food allergies and intolerance

  • Allergen avoidance
  • Referral to a dietician
  • Medication

Antihistamines can be helpful where food allergies cause symptoms such as itchy rashes (urticaria). Adrenaline may be prescribed in an injectable form if a person has a history of a severe allergic reaction (anaphylaxis).

MedicAlert® bracelets or necklaces (or similar) should be worn by people who have suffered anaphylaxis.


As the immune system matures and a child gets older, many grow out of allergies to eggs, wheat, milk and soya. Adults with food allergy may also grow out of their food allergy if an elimination diet is followed carefully. About a third of adults and children lose their reactions after 1-2 years of elimination diets. Allergic reactions to peanuts, seafood, fish and tree nuts rarely get better.

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